Transfer RNA is an integral part of the cell's protein synthesizing system. The biochemical reactions in which tRNA is involved are well documented. Nucleotide sequence analysis, proton NMR spectroscopy, and X-ray diffraction have been used to elucidate the structure of tRNA. However, the nature of the physical interaction of tRNA with other molecules involved in protein synthesis is essentially unknown. Carbon-13 NMR spectroscopy can be used to study structural and functional interactions of tRNA with other molecules and spectra would be more resolved than the corresponding proton NMR spectra. However, the natural abundance of carbon-13 is very low (1.1 atom %). We have specifically enriched tRNA in carbon-13 and began to use the (13C)-tRNA for structural and functional studies. Large quantities of tRNA will be enriched in vivo in carbon-13 methyl groups by growing a methionine auxotroph of Escherichia coli in medium with methionine-(methyl(13C)). Specific species of (13C)-enriched tRNA will be purified. Labeling the tRNA with (13C)-methyl groups is advantageous because such groups occupy specific, known sites in the tRNA nucleotide sequence, are natural to the molecule and create NMR spectral signals at regions of the spectrum free from ribose and major base interference. Other methods of carbon-13 enrichment of tRNA utilizing biological systems for the enrichment have proven successful. These include enrichment of the number 2 carbon of adenosine, cytosine and uracil in tRNA. Carbon-13 NMR spectroscopy of specific species of (13C)-enriched tRNA will be used to study the interaction of other nucleic acids and proteins with tRNA at the sites of (13C)-methyl groups, C2 of adenine, uracil and cytosine and other carbons.